Pipette tip for and method of automatically maintaining pipette tip depth in a fluid during a fluid transfer operation

ABSTRACT

A method for automatically maintaining a pipette tip depth in a conductive fluid during a fluid transfer operation, comprising the steps of: providing a pipetting device, comprising: a pipette tip; a first and a second electrode on the outer surface of the pipette tip; a frame supporting an actuator that is operatively connected to the pipette tip; and a controller that is in electrical connection with the first and second electrodes; providing a container fixed in height relative to the frame, the container holding a conductive fluid having a first liquid level; positioning the pipette tip in the container such that at least a portion of the first and second electrodes are submerged in the conductive fluid; measuring by the first and second electrodes a change in resistance relative to the conductive fluid; sending by the first and second electrodes a signal to the controller relative to the change.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of and claims priorityunder 35 U.S.C. § 120 to U.S. application Ser. No. 16/958,999, filed onJun. 29, 2020, the entire disclosure of which is incorporated herein byreference. This application is also related to U.S. Provisional PatentApp. No. 62/611,161, entitled “Pipette Tip for and Method ofAutomatically Maintaining Pipette Tip Depth in a Fluid During a FluidTransfer Operation,” filed on Dec. 28, 2017, the entire disclosure ofwhich is incorporated herein by reference.

TECHNICAL FIELD

The disclosed subject matter relates generally to liquid handlingmethods, and more particularly, to a pipette tip for and method ofautomatically maintaining pipette tip depth in a fluid during a fluidtransfer operation.

BACKGROUND

Automated liquid handling instruments include robots used to transferspecific quantities of liquids between designated containers. Suchinstruments are useful in a variety of applications including cellbiology, genomics, forensics, and drug research. The instruments assisthumans with the repetitive task of delivering liquids in a wide range ofvolumes by improving the speed and efficiency of the operations, andimproving the precision and accuracy of the delivered volumes.

A wide variety of labware containers are typically used in liquidhandling applications. Microtiter® plates containing an array of 96,384, or 1536 sample wells are quite common. Depending on the size andnumber of sample wells, such plates may hold somewhere between tens ofnanoliters to several milliliters of liquid. Also common are largercontainers, ranging from vials holding one to two milliliters of liquid,up to large tubes holding tens of milliliters or bottles holdinghundreds of milliliters. It can be easily understood that each uniquelabware container will have a unique relationship between volume ofliquid in the container and the height of the liquid surface in thecontainer.

The precision and accuracy of transferred volumes can be affected bymany factors. These factors can range from properties of the liquiditself, such as its viscosity or surface tension, to properties ofsystem components, such as the hydrophobicity of the pipette tip, oreven environmental conditions, such as ambient temperature and pressure.

In automated liquid handling, control variables of the instrument canhave a significant effect on the pipetted volumes. Such controlvariables include the speed of pump actuation, delay between the end ofpump actuation and removal of the pipette tip from the liquid, and/orspeed of pipette tip removal from the liquid. One prominent controlvariable that has a strong effect on pipetting performance is the depthto which the pipette tip is submerged under the surface of the liquidthroughout the operation. If the pipette tip is too shallow in theliquid, the vacuum of aspiration may lead to cavitation of the liquid atthe opening of the pipette tip, causing air to be aspirated rather thanthe liquid, and thus causing an error in the aspirated volume. If thepipette tip is too deep in the liquid, a larger surface area of thepipette tip is in contact with the liquid and a greater volume of liquidmay cling to the pipette tip as it is retracted from the liquid.Additionally, deeper submersion results in increased hydrostaticpressure at the opening of the pipette tip, which may cause variationsin the resulting pipetted volume. Thus, it is best to maintain thepipette tip at the optimal depth, even as the liquid level is changingwhile liquid is aspirated from or dispensed into a container. Further,it is important to ensure the depth of the pipette tip in the liquidthroughout a pipetting operation is consistent from one operation to thenext.

Methods for detecting the liquid level in the field of automated liquidhandling are common and well established in the art. However, none arecapable of tracking the liquid level using real time sensor feedback tomaintain the depth of the pipette tip during a pipetting operation. Inthe current state of the art, liquid level tracking is achieved bypredicting the expected liquid level change based on the requestedvolume and the geometry of the container. The geometry of the containerrefers to the cross sectional area as it relates to height in thecontainer. From this information, the height change associated with aparticular volume change can be calculated. This method requires thecontainer geometry to be characterized and programmed into theinstrument protocol prior to a pipetting operation. This requirement canrestrict the type of labware used with a particular instrument and addscomplexity to the process of programming an instrument for a particularpipetting operation. Moreover, these types of calculations assume thatthe pipetting operation will aspirate or dispense a uniform, equalvolume of liquid during each pipetting action, which may not be anaccurate assumption. If the calibration is slightly off, this error canbe compound over the course of the pipetting operation, and the actualliquid level may be correspond to the expected liquid level based on thecalculations. Consequently, new approaches are needed for tracking theliquid level during a pipetting operation without adding complexity tothe process.

An example of the conventional method of liquid level tracking is inU.S. Pat. No. 4,586,546, entitled “Liquid handling device and method,”issued on May 6, 1986. The '546 patent describes a device and method fordetecting the liquid level in a container and predicting the height ofliquid and the desired height of the pipette tip in the container aftera certain volume has been added or removed.

There are several other common methods of automatically detecting thelevel of liquid in a container. The simplest of these is based onpressure measurements. Changes in pressure inside the pipette tip aredetected as the pipette tip enters the surface of a liquid. This methoddoes not require any specialized pipette tip designs or features, and inmost cases is only viable if the pipette tip is empty. Pressure-basedliquid level detection could be performed using any conventional pipettetip. An example of a pressure-based liquid level detection method is inU.S. Pat. No. 4,794,085, entitled “Apparatus and method for detectingliquid penetration by a container used for aspirating and dispensing theliquid,” issued on Dec. 27, 1988. The '085 patent describes a pipettingdevice with a pressure sensor to measure pressure within the device. Thepipette tip is moved down toward the liquid in increments. At each stagea syringe pump is actuated to create a pressure differential within thedevice. If the pipette tip has entered liquid, the opening of thepipette tip will be blocked, and the pressure sensor may detect thepressure differential. Another example is in U.S. Pat. No. 8,287,806,entitled “Pipetting apparatus with integrated liquid level and/or gasbubble detection,” issued on Oct. 16, 2012. The '806 patent describes adevice for detecting liquid level using pressure measurements. Thispipetting device specifies the use of a system liquid, rather than air,between the pump and pipette tip.

The pipette tip design and composition can be enhanced to allow moreadvanced liquid surface sensing methods. Such enhancement typicallyinvolves providing an electrode in the pipette tip so electrical signalscan be used to detect the liquid level. The most common enhancement isto make the pipette tip out of electrically conductive plastic andmeasure capacitance between the conductive pipette tip and a groundplane below the containers holding liquids or samples. An example ofcapacitance-based liquid level detection is in U.S. Pat. No. 4,736,638,entitled “Liquid level sensor,” issued on Apr. 12, 1988. The '638 patentdescribes a device for sensing liquid levels in fluid transfermechanisms comprising a conductive member supporting containers ofsample liquids and a conductive pipette probe. A capacitance signal ismeasured between the probe and the supporting ground plane and a changein capacitance is detected when the probe touches a fluid.

The pipette tip design can be further enhanced by providing multipleelectrodes within the pipette tip to enable more advanced signaldetection. Capacitance can be measured between one or both electrodesand a bottom ground plane, capacitance could be measured between the twoelectrodes, or electrical impedance could be measured between the twoelectrodes. An example of an electrical signal based liquid leveldetection with pipette tips having more than one electrode is in U.S.Pat. No. 5,045,286, entitled “Device for aspirating a fixed quantity ofliquid,” issued on Sep. 3, 1991. The '286 patent describes a pipette tipwith two electrically conductive members arranged in the nozzle suchthat one electrode extends from the nozzle attachment to the lower endof the nozzle and the other electrode extends from the nozzle attachmentto a certain distance or height above the lower end of the nozzle, suchthat the distance or height corresponds to a fixed quantity of liquid tobe aspirated through the nozzle. The '286 patent also discloses variousways to produce such a pipette tip. Another example is in U.S. Pat. No.6,851,453, entitled “Fluid dispense verification system,” issued on Feb.8, 2005. The '453 patent describes a probe for fluid dispensing with twoelectrodes with ends longitudinally spaced from each other. A signal ismeasured between the two electrodes for the purposes of detecting thesurface of the liquid and fluid delivery verification. Yet anotherexample is in U.S. Pat. No. 5,550,059, entitled “Fluid sensing pipette,”issued on Aug. 27, 1996. The '059 patent describes a probe for fluiddispensing with two concentrically arranged conductive tubes insulatedfrom each other. A signal is measured between the two electrodes for thepurpose of detecting the surface of the liquid.

SUMMARY

Disclosed herein is a device, system, and method for pipettingapplications. In one aspect, a pipetting device for automaticallymaintaining a pipette tip depth in a conductive fluid during a fluidtransfer operation is described. The pipetting device comprises apipette tip having a securing end with an opening, a fluid transferringend with an opening, an outer surface, and an inner surface, wherein theouter surface includes an electrically insulating material; a first anda second electrode on the outer surface of the pipette tip, the firstand second electrode being separated by the electrically insulatingmaterial; a frame supporting an actuator that is operatively connectedto the pipette tip, wherein the pipette tip is vertically orientedrelative to the frame, and wherein the actuator is adapted to adjust aposition of the pipette tip relative to the frame; a controller that isin electrical connection with the first and second electrodes, whereinthe first and second electrodes are adapted to send the controller asignal relative to a conductive fluid that comes in contact with theouter surface of the pipette tip; and wherein the controller is adaptedto command the actuator to move the position of the pipette tip inresponse to the signal.

In some embodiments, each of a first and second electrode describedherein extends the full longitudinal length of the pipette tip from thesecuring end to the fluid transferring end. In other embodiments, eachof a first and second electrode described herein terminates at a pointnear the securing end, wherein the point is where the first and secondelectrodes are electrically connected to the controller. In someinstances, each of a first and second electrode described hereinterminates at a point near the fluid transferring end, wherein the pointis where conductive fluid can reach.

In some instances, a signal from a first and second electrode describedherein is a measurement of resistance relative to a conductive fluid. Afirst and second electrode described herein can be made of copper insome cases, or made of an electrically conductive polypropylene in othercases.

In some embodiments, a pipetting device further comprises first andsecond electrical points, and first and second electrical wiresconnecting the first and second electrodes, respectively, to acontroller.

In another aspect, a method for automatically maintaining a pipette tipdepth in a conductive fluid during a fluid transfer operation isdescribed herein. An exemplary method comprises the steps of: providinga pipetting device, comprising: a pipette tip having a securing end withan opening, a fluid transferring end with an opening, an outer surface,and an inner surface, wherein the outer surface includes an electricallyinsulating material; a first and a second electrode on the outer surfaceof the pipette tip, the first and second electrode being separated bythe electrically insulating material; a frame supporting an actuatorthat is operatively connected to the pipette tip, wherein the pipettetip is vertically oriented relative to the frame, and wherein theactuator is adapted to move the height of the pipette tip relative tothe frame; and a controller that is in electrical connection with thefirst and second electrodes; providing a container fixed in heightrelative to the frame, the container holding a conductive fluid having afirst liquid level; positioning the pipette tip in the container suchthat at least a portion of the first and second electrodes are submergedin the conductive fluid, wherein the positioning step forms a controlloop between the first and second electrodes, the actuator, thecontroller, and the conductive fluid; measuring by the first and secondelectrodes a change in resistance relative to the conductive fluid;sending by the first and second electrodes a signal to the controllerrelative to the change, wherein the controller is configured to commandthe actuator to move the pipette tip vertically in response to thesignal.

In some instances, a method described herein can further comprise thesteps of: aspirating by the pipette tip an amount of the conductivefluid, wherein the conductive fluid has a second liquid level followingthe aspirating step; commanding by the controller the actuator to movethe pipette tip relative to the second liquid level such that the firstand second electrodes remain submerged in the conductive fluid. In someinstances, a method described herein can further comprise the steps of:dispensing by the pipette tip an amount of the conductive fluid, whereinthe conductive fluid has a second liquid level following the dispensingstep; commanding by the controller the actuator to move the pipette tiprelative to the second liquid level such that the first and secondelectrodes remain submerged in the conductive fluid.

In some embodiments, a method described herein can further comprise thestep of: maintaining by the control loop the pipette tip at a constantsecond liquid level relative to the liquid surface of the conductivefluid.

In yet another aspect, a pipette tip is described herein comprising abody made from an electrically insulating material, the body comprising:an outer surface, and an inner surface; a first electrode disposed onthe outer surface; and a second electrode disposed on the outer surface,the second electrode being separated from the first electrode by theelectrically insulating material.

In some cases, a body described herein further comprises an apparatussecuring end; and a fluid transferring end positioned opposite theapparatus securing end, the fluid transferring end comprising a fluidtransferring opening.

In some embodiments, a pipette tip described herein can further comprisea third electrode and a fourth electrode disposed on the inner surface.

Each or all of the electrodes described herein can extend along a fulllongitudinal length of the body from the fluid transferring end to theapparatus securing end in some cases. In other cases, each or all of theelectrodes extend a distance less than a full longitudinal length of thebody from the fluid transferring end to the apparatus securing end.

Each of the electrodes described herein, can in some instances, be madeof copper or an electrically conductive polypropylene.

In some embodiments, each electrode described herein can comprise anelectrical contact tab positioned on the apparatus securing end of theelectrode. In some instances, the electrical contact tab can extend toan end of the apparatus securing end, or can extend beyond the apparatussecuring end of the pipette tip.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the disclosed subject matter in general terms,reference will now be made to the accompanying Drawings, which are notnecessarily drawn to scale, and wherein:

FIG. 1 illustrates a cross-sectional side view of a liquid handlingapparatus according to an exemplary embodiment of the presentlydisclosed subject matter;

FIG. 2A, FIG. 2B, and FIG. 2C illustrate a side view, a perspectiveview, and a cross-sectional view, respectively, of a pipette tipaccording to an exemplary embodiment of the presently disclosed subjectmatter;

FIG. 3A illustrates a cross-sectional view of a pipette tip attached toa liquid handling apparatus according to an exemplary embodiment of thepresently disclosed subject matter;

FIG. 3B illustrates an exploded side view of a pipette tip for attachingto a liquid handling apparatus according to an exemplary embodiment ofthe presently disclosed subject matter;

FIG. 4A illustrates a schematic diagram of the liquid handling apparatusof FIG. 1 with a pipette tip attached thereto according to an exemplaryembodiment of the presently disclosed subject matter;

FIG. 4B illustrates a side view of the liquid handling apparatus of FIG.1 with a pipette tip attached thereto according to an exemplaryembodiment of the present subject matter;

FIG. 5A shows a plot of a measured signal and system response duringaspiration of a sample using the device according to an exemplaryembodiment of the present subject matter;

FIG. 5B shows a plot of a measured signal and system response duringdispensation of a sample using the device according to an exemplaryembodiment of the present subject matter;

FIG. 6A, FIG. 6B, and FIG. 6C illustrate side views of an exemplarypipette tip at different levels, heights, or depths with respect to thelevel of liquid;

FIG. 7 illustrates a flow diagram of an example of a method of using theliquid handling apparatus of FIG. 1 to adjust automatically the depth ofthe pipette tip in a liquid in response to a changing probe resistancemeasurement;

FIG. 8A, FIG. 8B, FIG. 8C, FIG. 8D, and FIG. 8E illustrate various viewsof a 20 μL-pipette tip according to another exemplary embodiment of thepresently disclosed subject matter;

FIG. 9A, FIG. 9B, FIG. 9C, FIG. 9D, and FIG. 9E illustrate various viewsof a 20 μL-pipette tip according to yet another exemplary embodiment ofthe presently disclosed subject matter;

FIG. 10A, FIG. 10B, FIG. 10C, FIG. 10D, and FIG. 10E illustrate variousviews of a 200 μL-pipette tip according to yet another exemplaryembodiment of the presently disclosed subject matter;

FIG. 11A, FIG. 11B, FIG. 11C, FIG. 11D, and FIG. 11E illustrate variousviews of a 200 μL-pipette tip according to yet another exemplaryembodiment of the presently disclosed subject matter; and

FIG. 12A, FIG. 12B, FIG. 12C, FIG. 12D, and FIG. 12E illustrate variousviews of a pipette tip according to still another exemplary embodimentof the presently disclosed subject matter.

DETAILED DESCRIPTION

The following subject matter now will be described more fullyhereinafter with reference to the accompanying Drawings, in which some,but not all embodiments of the disclosed subject matter are shown. Likenumbers refer to like elements throughout. The disclosed subject mattermay be embodied in many different forms and should not be construed aslimited to the embodiments set forth herein; rather, these embodimentsare provided so that this disclosure will satisfy applicable legalrequirements. Indeed, many modifications and other embodiments of thedisclosed subject matter set forth herein will come to mind to oneskilled in the art to which the disclosed subject matter pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated Drawings. Therefore, it is to be understood that thedisclosed subject matter is not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.

In some embodiments, the disclosed subject matter provides a pipette tipfor and method of automatically maintaining pipette tip depth in a fluidduring a fluid transfer operation. The pipette tip and methods describedherein can provide automatic tracking of a liquid level in real timeduring a pipetting operation without prior knowledge of the containergeometry. Namely, the presently disclosed pipette tip and method canreduce or eliminate the need for prior knowledge and characterization oflabware containers for the purpose of predicting changes in the heightof a liquid surface during a pipetting operation.

The present disclosure provides a method of maintaining a depth of apipette tip in a liquid throughout a pipetting operation, as the liquidsurface rises or falls in its container, without any prior knowledge ofthe container geometry. For instance, in a laboratory setting, a userwith no knowledge of, or experience programming a liquid handler for usewith particular labware containers, can easily work with an automatedliquid handler on which a pipette tip and method disclosed herein havebeen implemented. The user may benefit from improved ease of useaccompanied by improved precision and accuracy of transferred volumesresulting from the consistent and reliable depth of a pipette tipthroughout a series of liquid handling operations.

In some embodiments, a pipette tip and method described herein have asensing mechanism in the pipette tip to track the surface of a liquidwith respect to the pipette tip during a pipetting operation on anautomated liquid handling instrument. Namely, a pipette tip describedherein comprises a pair of electrodes positioned along a length of thepipette tip. The pair of electrodes can provide electrical feedback(e.g., an electrical resistance measurement between electrodes) that canbe correlated to a depth of the pipette tip in a conductive fluid. Thatis, a resistance value between the pipette tip electrodes will changeproportionally with the depth of the pipette tip in the fluid.

In some embodiments, a pipette tip and method described herein canimprove ease of use of automated liquid handling instruments whilemaintaining or improving the reliability of pipetting results.

In some embodiments, a pipette tip and method described herein canimprove a user experience of automated liquid handling instruments byautomating some aspects of pipetting operations that may otherwisenecessitate manual programming of the instrument by the user. Inparticular, the pipette tip and method can remove or reduce a need todefine and specify a geometry of labware containers by providing amethod of automatically tracking the liquid level in real time during apipetting operation. Further, a pipette tip and method described hereincan in many instances eliminate a need for prior knowledge andcharacterization of labware containers for the purpose of predictingchanges in the height of the liquid surface as liquid is added orremoved from a container.

In some embodiments, a pipette tip and method described herein providesa pipette tip that is substantially transparent, whereby the user maydirectly observe any liquid inside the pipette tip during a pipettingoperation.

Referring now to FIG. 1 is a side view of an example of a liquidhandling apparatus 1 for utilizing a pipette tip and method describedherein. Namely, liquid handling apparatus 1 is a mechanized liquidhandling device. Liquid handling apparatus 1 comprises a pump 2 influidic communication with a nozzle 3 via an enclosed air volume 4. Insome embodiments, the enclosed volume can be filled with a system fluid.The nozzle 3 has an opening 32 through which liquids are taken up intoor ejected out of the nozzle 3. Further, in some embodiments, the liquidhandling apparatus 1 can be fixed to a vertically oriented linearactuator 5 which can control the height of the nozzle 3 relative to afixed frame 54 of the apparatus 1 and relative to a container 6 fixed inheight relative to the fixed frame 54. However, in other instances, thelinear actuator 5 can be fixed in other orientations, such as obliquelyor diagonally to the fixed frame 54. The container 6 holds a quantity ofliquid 61. The linear actuator 5 can be used to adjust the height of theliquid handling apparatus 1 in order to insert the nozzle 3 into theliquid 61 so that it can aspirate or dispense the liquid 61.

As liquid 61 is removed from or added to the container 6 via the nozzle3, the surface of the liquid (i.e., liquid surface 62) in the container6 will fall or rise, respectively. The height of the liquid handlingapparatus 1 must be adjusted in order to keep the opening of the nozzle3 submerged in the liquid 61 at a consistent depth as the liquid levelchanges to avoid transfer volume errors caused by aspirating air.Preferably, the height of the liquid handling apparatus 1 is controlledsuch that the opening of the nozzle 3 remains at a consistent depthbelow the liquid surface 62 as the liquid level changes for maximumprecision and accuracy of delivered volumes.

In an automated pipetting application, the nozzle 3 can be referred toas a pipette tip. Accordingly, the nozzle 3 is hereafter called thepipette tip 3. In one embodiment of the presently disclosed method,electrical signal feedback from the pipette tip 3 can be used to sensethe depth of the pipette tip 3 in the liquid 61. This signal feedbackcan serve as input to a control loop driving the vertical linearactuator 5 to maintain a constant depth of the pipette tip 3 in theliquid 61, even as the liquid level rises and falls in the container 6.

The method disclosed herein can make use of the electrical resistivityof conductors in the pipette tip 3. In one such exemplary embodiment,the pipette tip 3 can include pipette tip electrodes 31 a, 31 b toprovide this electrical input. Electrical resistivity is an intrinsicmaterial property that describes the degree to which a material opposesthe flow of electric current. The total electrical resistance of a bodyof material is related to its resistivity and geometry, as calculatedby:

$R = {\rho \cdot \frac{l}{A}}$

-   -   Where:        -   R is the resistance (ohms)        -   ρ is the resistivity (ohm-metre)        -   l is the length of the body between points of electrical            contact (meter)        -   A is the cross-sectional area of the body (meter square)

Thus, it can be understood that by changing the length of a body throughwhich electric current flows, the measured resistance of the body willchange proportionally.

FIG. 2A, FIG. 2B, and FIG. 2C is a side view, a perspective view, and across-sectional view, respectively, of one embodiment of a pipette tip 3that includes a liquid level sensing mechanism. Conductive electrodes(e.g., pipette tip electrodes 31 a, 31 b) with measurable resistance canbe provided in a liquid handling pipette tip 3. Namely, two separatepipette tip electrodes 31 a, 31 b are included on the pipette tip 3 tomeasure a resistance in the disclosed method. In some embodiments, thetwo pipette tip electrodes 31 a, 31 b extend a full longitudinal lengthof the pipette tip 3 from a securing end 33 to a fluid transferring end34. For orientation purposes, the fluid transferring end 34 comprisesopening 32 of the pipette tip 3, where liquids are aspirated into, anddispensed from, the pipette tip 3. The securing end 33 is locatedopposite to the fluid transferring end (i.e. distal to the opening 32),and is the portion of the pipette tip 3 that interacts with, and/orsecures the pipette tip 3 to a liquid handling apparatus 1. In someembodiments, the two pipette tip electrodes 31 a, 31 b do not extend thefull longitudinal length of the pipette tip 3, but instead can terminatebelow the securing end 33 of the pipette tip 3. Thus, in some instancesone or both of the pipette tip electrodes 31 a, 31 b have a length thatis less than the full longitudinal length of the pipette tip 3.Preferably, the two pipette tip electrodes 31 a, 31 b should terminatenear the securing end 33 of the pipette tip 3 where an electricalconnection to the liquid handling apparatus 1 will be made. The designof such an electrical connection can vary. In some embodiments, the twopipette tip electrodes 31 a, 31 b can terminate above the fluidtransferring end 34 of the pipette tip 3. However, it should beunderstood that no liquid level tracking is possible below a point onthe pipette tip 3 to which both pipette tip electrodes 31 a, 31 bextend. In order to comply with general practice ensuring best fluidtransfer results, only a very small length of the pipette tip 3 issubmerged in a fluid (e.g., liquid 61). Thus, the two pipette tipelectrodes 31 a, 31 b preferably extend to or nearly to the fluidtransferring end 34 of the pipette tip 3 to allow for liquid leveltracking.

In some embodiments, pipette tip electrodes 31 a, 31 b are fullyseparated from one another by electrically insulating material 37.Further, both pipette tip electrodes 31 a, 31 b are exposed to a pipettetip outer surface 36 to allow sensation of the liquid level outside thepipette tip 3, and neither conductor is exposed to a pipette tip innersurface 35 to prevent sensation of the liquid level inside the pipettetip 3.

However, the design of the pipette tip 3 is not limited only toelectrodes on the outer surface thereof. Instead, the electrodes can bepositioned on any surface of the pipette tip 3 not inconsistent with theobjectives of this disclosure. For example, in some embodiments, thepipette tip electrodes 31 a, 31 b can be provided on the pipette tipinner surface 35 to allow sensation of the liquid level inside thepipette tip 3. Namely, to measure a liquid level inside a calibratedpipette tip 3 and therefore measure the volume of a calibratedconductive liquid. In yet other embodiments, the design of the pipettetip 3 includes electrodes on both the outer surface and the innersurface of the tip. Accordingly, such a design allows sensation of theliquid level both outside and inside the pipette tip 3.

In some embodiments, a pipette tip 3 described herein is disposable toavoid contamination from one process to another. In some instances, thepipette tip 3 is resistant to a wide range of chemicals. For example, insome cases the pipette tip 3 is an injection molded product composed ofpolypropylene. Since polypropylene is an excellent electrical insulator,this material can also serve as an appropriate insulating material toseparate the two pipette tip electrodes 31 a, 31 b. However, theinvention is not limited to pipette tips 3 made solely frompolypropylene, but, rather, any material not inconsistent with theobjectives of this disclosure can also be used. For example, in someembodiments, pipette tips 3 described herein can be made frompolyethylene, polybutylene, or other polyolefins. The following methodswill be described in the context of polypropylene as a building materialfor the pipette tip 3 for purposes of simplicity and readability, butthe invention should not be interpreted as excluding other suitablematerials.

One method of making a pipette tip with two conductive electrodes isdual shot injection molding, comprising a first shot of transparentinsulating polypropylene material to form the body and inner cone of thepipette tip 3, and a second shot of electrically conductivepolypropylene to form the two separate conductive pipette tip electrodes31 a, 31 b. The result is a single part or unit composed of twodifferent materials. Polypropylene is an excellent electrical insulator,and so is an appropriate insulating material for the first shot to formthe body of the pipette tip 3 and separate the two pipette tipelectrodes 31 a, 31 b. Polypropylene can be made to be electricallyconductive through the addition of a variety of conductive additives,such as conductive carbon black or various inorganic conductors known tothose in the art. Accordingly, polypropylene is an appropriate materialfor the second shot to form the two separate conductive pipette tipelectrodes 31 a, 31 b.

Another method of making a pipette tip with two conductive electrodes asdescribed above is to selectively coat the outside of a pipette tip witha conductive material. This could involve printing a conductive ink orapplying a conductive resin, among other techniques. In a preferredembodiment, the body of the pipette tip 3 is composed of electricallyinsulating polypropylene and is produced by an injection moldingprocess. Conductive electrodes are applied to the pipette tip in asecondary process, in which conductive polypropylene is printed onto theoutside of the pipette tip to form thin conductive strips. One advantageof such a method is that the conductive strips can cover a very smallarea of the outside of the pipette tip, leaving much of the pipette tiptransparent to an observer. In some instances, transparency can be adesirable feature of the pipette tip for the user of a liquid handlingdevice because it allows the user to directly observe any liquid insidethe pipette tip during a pipetting operation. Conventional conductivepipette tips are fully opaque and the liquid inside of the pipette tipcannot be observed.

Examples of the material for forming the conductive pipette tipelectrodes 31 a, 31 b of the pipette tip 3 can include, but are notlimited to, electrically conductive polypropylene resin, electricallyconductive epoxy, electrically conductive ink, copper, and the like.Further, the conductive material used to form the conductive pipette tipelectrodes 31 a, 31 b has an appropriate resistivity such that, giventhe length and cross section of the electrode body, the total resistancecan be measured with reasonable resolution. For example, conductorscomposed of copper metal wires applied to the pipette tip outer surface36 can have an inconsequential resistivity to allow measurable changesin resistance over the length of a pipette tip 3 without highlyspecialized equipment. A typical total resistance measurement of apipette tip that can hold 200 μL of liquid and has electrodes composedof conductive polypropylene resin and with the fluid transferring end 34submerged about 2 millimeters into tap water can be on the order of fromabout 50 kiloohm to about 200 kiloohm. The allowable range of resistanceis much greater.

Referring now to FIG. 3A is a block diagram showing the attachment of apipette tip 3 described herein to a liquid handling apparatus 1.Additionally, FIG. 3B shows a side view of a specific example of thepipette tip 3 adapted for attachment to a liquid handling apparatus 1.In an embodiment shown in FIGS. 3A and 3B, a pipette tip attachmentpoint 12 of liquid handling apparatus 1 includes a pair of electricalcontact points 11 a, 11 b to conduct electrical signals between the pairof pipette tip electrodes 31 a, 31 b, respectively, and wires 13 leadingto an electronic controller 7. During pipette tip 3 attachment, each oftwo electrical contact points 11 a, 11 b comes into good electricalconnection with its corresponding pipette tip electrode 31 on thepipette tip 3, so that both pipette tip electrodes 31 a, 31 b on thepipette tip 3 are connected to the electronic controller 7 by theelectrical contact points 11 a, 11 b. Specifically, electrical contactpoint 11 a is connected to pipette tip electrode 31 a and electricalcontact point 11 b is connected to pipette tip electrode 31 b. Theelectrical contact points 11 a, 11 b can be spring loaded to ensure areliable electrical connection is made to the pipette tip electrodes 31a, 31 b each time a pipette tip 3 is attached to the liquid handlingapparatus 1. In some embodiments, a mechanism or method is implementedto ensure the pipette tip 3 is reliably attached to the liquid handlingapparatus 1 in an appropriate orientation such that the electricalcontact points 11 a, 11 b are in good electrical connection to thepipette tip electrodes 31 a, 31 b. Further, the pipette tip 3 attachesto the liquid handling apparatus 1 by a mechanism that ensures reliablepneumatic sealing to a conduit leading to a pump 2 to ensure properpipette performance. As previously described herein, the pipette tip 3attaches to the liquid handling apparatus 1 at the securing end 33. Thedesign and direction of such mechanisms and methods can vary and theirspecific features fall outside the scope of the present disclosure.

With no pipette tip 3 attached to the liquid handling apparatus 1, thecircuit between the two electrical contact points 11 a, 11 b on theliquid handling apparatus 1 is open and no current can flow. That is,the measured resistance is extremely high. With an appropriate pipettetip 3 properly attached to the liquid handling apparatus 1, the circuitbetween the two electrical contact points 11 a, 11 b will still be open,however a slight change in signal can be detected between the twoconductors, and thus the presence of a properly attached pipette tip 3can be confirmed before proceeding with a pipetting operation.

During a pipetting operation, if the pipette tip 3 is submerged in aconductive fluid, the pipette tip electrodes 31 a, 31 b provided in thepipette tip 3 will be electrically connected via the conductive fluid.If such a connection is made, it will be a probe-liquid closed circuitbetween the electronic controller 7, the electrical contact points 11 a,11 b at the pipette tip attachment point 12, the pipette tip electrodes31 a, 31 b, and the conductive fluid 61, causing a significant change insignal measured by the electronic controller 7. If the depth of thepipette tip 3 in the liquid changes, the point along the length of thepipette tip 3 at which the conductive fluid is connecting the twopipette tip electrodes 31 a, 31 b will change, and therefore theeffective length of the pipette tip electrodes 31 a, 31 b in the circuitwill change. Thus, the resistance of pipette tip electrodes 31 a, 31 bin the circuit will change proportionally with the depth of the pipettetip 3 in the fluid (e.g., liquid 61).

A particular depth can be maintained if a reference resistance value istaken at that particular depth. Continuous resistance measurements canbe used as input to a control loop driving the vertical linear actuator5 tuned to maintain the reference resistance value at a set point. Ifthe liquid level rises or falls on the pipette tip, the resistancemeasurement will fall or rise, respectively, and the height of thepipette tip 3 can be adjusted to maintain that resistance value, andtherefore maintain the depth of the pipette tip 3 as the liquid levelchanges.

Resistance measurement of the probe-liquid circuit can be performed in avariety of ways, as one familiar with the art will understand. In someembodiments, the unknown resistance of the pipette tip circuit can bemeasured with reference to a known input voltage and a known resistanceby way of a voltage divider circuit and an analog-to-digital signalprocessing unit.

The input signal to be measured can be generated in the form of directcurrent or alternating current. In some embodiments, an alternatingcurrent signal is used to improve the performance of the system. In someembodiments that make use of a direct current signal, the conductivityof a pipette tip electrode 31 submerged in conductive liquid candeteriorate over a certain period of time in ionic liquids. The use ofalternating current has been found to prevent this fouling of thepipette tip electrodes.

In some embodiments, an alternating current voltage signal can be simplyinterpreted as a direct current voltage by taking the root mean squareof the alternating current voltage signal before conventionalanalog-to-digital signal processing. In a preferred embodiment, thealternating current signal is interpreted by way of lock-inamplification. Such a method is capable of extracting a signal with aknown reference frequency even from very noisy input. Such a method iseffective at isolating the desired signal even in the midst ofinterference from adjacent apparatuses performing similar or differentfunctions. The resulting direct current signal can be processed by atypical analog to digital conversion.

The method described herein is only compatible with conductive liquidsthat allow current to flow between the pipette tip electrodes 31 a, 31b. For non-conductive fluids, conventional liquid level tracking isrequired, meaning the labware geometry must be programmed in advance topredict liquid level movements during a pipetting operation. However,the method described herein can be implemented as a fast and convenientway of calibrating the geometry of labware containers to be used in apipetting operation with non-conductive fluids. The calibration methodwould involve measuring the container geometry by liquid level detectionand tracking with a conductive fluid. Such a calibration method would befree of cumbersome measurements to determine container geometry. Thecalibrated geometry can be useful for performing liquid level trackingwith non-conductive liquids as well as with conventional pipette tipslacking the dual electrode features described herein.

An example of the disclosed method of automatically tracking the surfaceof a liquid during a pipetting operation with a pipette tip, such as thepipette tip 3 as described hereinabove with reference to FIG. 1 throughFIG. 3B, will now be described in detail with reference to FIG. 4A andFIG. 4B.

Referring now to FIG. 4A, a block diagram is shown of the liquidhandling apparatus 1 of FIG. 1 with a pipette tip 3 attached thereto.Additionally, FIG. 4B shows a side view of a specific example of oneinstantiation of the liquid handling apparatus 1 of FIG. 1 with apipette tip 3 attached thereto.

As illustrated, a liquid handling apparatus 1 described herein includes,but is not limited to, a pump 2, a pipette tip 3 as described above (inFIG. 1 through FIG. 3B) in airtight connection to a conduit leading tothe pump 2, an electronic controller 7 governing the apparatus 1 inelectrical connection with the pipette tip electrodes 31 a, 31 b, and avertical linear actuator 5, which can move the apparatus 1 vertically.The pump 2 can be any mechanism that provides positive or negativepressure. In one example, the pump 2 can be a syringe pump, wherein thesyringe pump 2 can include, but is not limited to, a motor 21, a syringe22, a linear motion guide 23, and a lead screw 24, as shown in FIG. 4Aand FIG. 4B. The vertical linear actuator 5 can include, but is notlimited to, a motor 51, a linear motion guide 52, a lead screw 53, andan attachment to the fixed frame 54 of the apparatus 1, as shown in FIG.4A and FIG. 4B. The electronic controller 7 can be a microcontrollercapable of, but not limited to, generating and receiving signals,processing the signals, sending motion commands, and processing data inorder to perform the electronic functions described herein as well asother features.

In some embodiments, a method described herein begins with theelectronic controller 7 measuring a resistance between electricalcontact points 11 a, 11 b at the pipette tip attachment point 12 toidentify whether an appropriate pipette tip 3 has been correctlyconnected to the system. If an appropriate pipette tip 3 has beencorrectly connected, the method can continue.

In some embodiments, a method described herein proceeds by lowering thepipette tip 3 to the liquid surface 62 (shown in FIG. 1 ) using anyautomated method known in the art. For example, the pipette tip 3 islowered into the liquid to a desired depth. The desired depth istypically a depth sufficient to ensure that air will not be aspirated.For example, the end of the pipette tip 3 can be from about 1 mm toabout 2 mm below the liquid surface 62. The electrical controller 7 thenmeasures the resistance of the pipette tip 3 to determine a referenceresistance value to be used as a set point in the vertical positioncontrol loop. If the liquid 61 is found to be non-conductive, theautomatic tracking method is cancelled and the geometry of the container6 must be programmed into the instrument to ensure proper tracking.

In some embodiments, the depth of the pipette tip 3 in the liquid 61 ismaintained by a vertical position control loop that uses the resistancemeasurement as input. A typical resistance signal and associatedvertical actuator response during an aspiration is shown in a plot 200of FIG. 5A. The control loop drives the vertical linear actuator 5 tomaintain a reference resistance set point 81 a of the pipette tip 3shown in plot 200. If the liquid level in the container falls, theliquid level on the pipette tip 3 also falls and the resistancemeasurement increases. In some instances, an increase in resistance atthe pipette tip 3 is interpreted as a reduction in the AID countmeasured by the electronic controller 7. If the resistance measurementincreases beyond a threshold 82 a shown in plot 200, meaning the A/Dcount drops below threshold 82 a, the electronic controller 7 willrespond by commanding the vertical linear actuator 5 to drive thepipette tip 3 downward to a Z position at a threshold level 83 a so asto track the liquid level and attempt to maintain the referenceresistance set point 81 a. The height of the liquid 61 in the container6 will only change as long as the pump 2 is aspirating liquid into thepipette tip 3. As the aspiration nears completion, the liquid level onthe pipette tip 3 will become stable and return to the set point 84shown in plot 200, causing the pipette tip to become stable at a Zposition corresponding with a new liquid level 85 shown in plot 200.

A typical resistance signal and associated vertical actuator response 5during a dispensation is shown in a plot 210 of FIG. 5B. After areference resistance set point 81 b has been established, if the liquidlevel in the container rises, the liquid level on the pipette tip risesand the resistance measurement decreases. A decrease in resistancecauses an increase in the A/D count measured by the electroniccontroller 7. If the A/D signal exceeds a threshold level 82 b, theelectronic controller 7 responds by commanding the vertical linearactuator 5 to drive the pipette tip 3 upward to a Z position at athreshold level 83 b so as to track the liquid level in an attempt tomaintain the reference resistance set point 81 b.

Those familiar in the art will understand a variety of control looptechniques can be applied. For example, the control loop can becontrolled in a proportional manner, meaning a small slow change inresistance signal will result in a small gradual change in Z position,and a large fast change in resistance will result in a fast change in Zposition.

Further to the example, FIG. 6A, FIG. 6B, and FIG. 6C show side views ofan example of the pipette tip 3 at different levels, heights, or depthswith respect to the level of liquid 61 (i.e., liquid surface 62).Namely, FIG. 6A shows the pipette tip 3 at a reference depth D_(R),which is, for example, the desired depth to which the pipette tip 3 isto be maintained during the pipetting process. The pipette tip 3 has aprobe resistance value R_(P). When at the reference depth D_(R) thepipette tip 3 has a certain probe resistance value R_(P) that can bemeasured and logged as the reference probe resistance value R_(P). Then,as the level of liquid 61 changes and the measured probe resistancevalue R_(P) changes, the Z position of the pipette tip 3 can be adjustedup or down until the reference depth D_(R) and the reference proberesistance value R_(P) are found. For example, FIG. 6B shows the pipettetip 3 at a depth that is less than the reference depth D_(R).Accordingly, the probe resistance value R_(P) is greater than thereference probe resistance value R_(P), which prompts the electroniccontroller 7 to adjust the Z position of the pipette tip 3 downwarduntil the reference depth D_(R) is reached. Similarly, FIG. 6C shows thepipette tip 3 at a depth that is greater than the reference depth D_(R).Accordingly, the probe resistance value R_(P) is less than the referenceprobe resistance value R_(P), which prompts the electronic controller 7to adjust the Z position of the pipette tip 3 upward until the referencedepth D_(R) is reached.

FIG. 7 shows a flow diagram of an example of a method 300 of using aliquid handling apparatus described herein to adjust automatically adepth of a pipette tip in a liquid in response to a changing proberesistance measurement. Accordingly, method 300 can be used toautomatically maintain the depth of the pipette tip 3 in a liquidthroughout a pipetting operation, as the liquid surface rises or fallsin its container, and with or without any prior knowledge of thecontainer geometry. The method 300 can include, but is not limited to,the following steps.

At a step 310, a pipetting device is provided that has a mechanism forsensing the liquid level in the pipette tip thereof. For example, theliquid handling apparatus 1 and a pipette tip 3 described herein areprovided, wherein the pipette tip 3 includes two pipette tip electrodes31 a, 31 b along the length of the pipette tip 3. The two pipette tipelectrodes 31 a, 31 b provide electrical feedback (e.g., an electricalresistance measurement between electrodes), such as a probe resistancevalue R_(P) (see FIG. 6A, FIG. 6B, FIG. 6C) that can be correlated to adepth of the pipette tip in a conductive fluid. That is, the resistanceof the pipette tip electrodes will change proportionally with the depthof the pipette tip in the liquid.

At a step 315, a container is provided that holds a conductive fluid tobe processed. For example, in the liquid handling apparatus 1, thecontainer 6 is provided that holds a quantity of liquid 61.

At a step 320, the pipette tip of the pipetting device is positioned inthe container such that its liquid level sensing mechanism is submergedin the conductive fluid at a desired and known depth. For example andreferring now to FIG. 6A, the pipette tip 3 of the liquid handlingapparatus 1 is positioned in the container 6 such that the pipette tip 3is submerged in the conductive fluid 61 at a desired and known depth,such as at the reference depth D_(R).

At a step 325, the reference probe resistance measurement is capturedand logged. For example and referring now to FIG. 6A, using theelectronic controller 7, the reference probe resistance value R_(P) ismeasured and logged.

At a step 330, pipetting operations are performed using the pipettingdevice that has the mechanism for sensing the liquid level in thepipette tip thereof. For example, pipetting operations are performedusing the pipette tip 3 of the liquid handling apparatus 1. In so doing,the liquid level in the container can rise or fall with respect to the Zposition of the pipette tip 3 in the conductive fluid 61. Further, inthis step the electronic controller 7 continuously monitors the proberesistance value R_(P) (see FIG. 6A, FIG. 6B, FIG. 6C) of the pipettetip 3.

At a step 335, the position of the pipette tip of the pipetting devicein the container is adjusted based on the current probe resistancemeasurement in comparison with the reference probe resistancemeasurement. In one example and referring now to FIG. 6B, if the liquidlevel has fallen with respect to the pipette tip 3, then the currentprobe resistance value R_(P) increases. In response to the increasingprobe resistance value R_(P), the electronic controller 7 adjusts the Zposition of the pipette tip 3 downward until the reference proberesistance value R_(P) is reached because the reference depth D_(R) isreached. In another example and referring now to FIG. 6C, if the liquidlevel has risen with respect to the pipette tip 3, then the currentprobe resistance value R_(P) decreases. In response to the decreasingprobe resistance value R_(P), the electronic controller 7 adjusts the Zposition of the pipette tip 3 upward until the reference proberesistance value R_(P) is reached because the reference depth D_(R) isreached.

Further and referring now to FIG. 1 through FIG. 7 , while multipleconductive bodies within a pipette tip can be known and measurement ofresistance between those bodies to determine some state of the nozzlerelative to the liquid can be known, a pipette tip and method describedherein can provide a mechanism for measuring resistance as an analoginput to a position control loop to maintain a certain predetermineddepth of the nozzle (i.e., the pipette tip 3) in the liquid. Bycontrast, conventional methods are limited in that any resistancemeasurement between two conductive bodies in a nozzle is taken as anon/off digital measurement to determine one of two states.

Further and referring now to FIG. 1 through FIG. 7 , a pipette tip andmethod described herein can provide certain beneficial features that arenot present in conventional liquid handling systems. For example,certain features of the conductive bodies can include, but are notlimited to, two conductive bodies on the outer surface of the pipettetip, both extending substantially the full length of the pipette tip.Namely, the two conductive bodies can extend from the top (securingend), where the tip is electrically and pneumatically connected to theapparatus, to the bottom (fluid transferring end), where the tip issubmerged in a fluid. Similarly, certain features of the conductivebodies can include, but are not limited to, two conductive bodies on theinner surface of the pipette tip, both extending substantially the fulllength of the pipette tip.

FIG. 8A, FIG. 8B, FIG. 8C, FIG. 8D, and FIG. 8E show various views ofthe pipette tip 3 according to another exemplary embodiment of thepresently disclosed subject matter. Namely, FIG. 8A is a perspectiveview, FIG. 8B is a top view, FIG. 8C is a side view, FIG. 8D is an endview from the tip end, and FIG. 8E is an end view from the wide end ofthe pipette tip 3. The pipette tip 3 shown in FIG. 8A, FIG. 8B, FIG. 8C,FIG. 8D, and FIG. 8E is one example of a 20 μL pipette tip. While thisexample is in the context of a 20 μL pipette tip, this particular sizeis merely exemplary, and other sizes consistent with the objectives ofthis disclosure are also contemplated.

The 20 μL-pipette tip 3 includes the pair of conductive electrodes(e.g., the pipette tip electrodes 31 a, 31 b). In this example, thepipette tip electrodes 31 a, 31 b are narrow electrodes that runsubstantially along the full length of the 20 μL-pipette tip 3 and onthe outside surface of the 20 μL-pipette tip 3. Further, each of thepipette tip electrodes 31 terminate near the securing end 33 of the 20μL-pipette tip 3 via a tab (or ear) 30. Namely, the pipette tipelectrode 31 a terminates via a tab (or ear) 30 a. Likewise, the pipettetip electrode 31 b terminates via a tab (or ear) 30 b. The tabs (orears) 30 a, 30 b extend beyond the securing end 33 of the 20 μL-pipettetip 3. The tabs (or ears) 30 a, 30 b provide the electrical connectionbetween the 20 μL-pipette tip 3 and the liquid handling apparatus 1.Again, the pipette tip electrodes 31 a, 31 b are fully separated fromone another by electrically insulating material 37.

FIG. 9A, FIG. 9B, FIG. 9C, FIG. 9D, and FIG. 9E show various views ofthe pipette tip 3 according to another exemplary embodiment of thepresently disclosed subject matter. Namely, FIG. 9A is a perspectiveview, FIG. 9B is a top view, FIG. 9C is a side view, FIG. 9D is an endview from the tip end, and FIG. 9E is an end view from the wide end ofthe pipette tip 3. The pipette tip 3 shown in FIG. 9A, FIG. 9B, FIG. 9C,FIG. 9D, and FIG. 9E is another example of a 20 μL pipette tip.

The 20 μL-pipette tip 3 shown in FIG. 9A, FIG. 9B, FIG. 9C, FIG. 9D, andFIG. 9E is substantially the same as the 20 μL-pipette tip 3 shown inFIG. 8A, FIG. 8B, FIG. 8C, FIG. 8D, and FIG. 8E except that the tabs (orears) 30 a, 30 b do not extend beyond the securing end 33 of the 20μL-pipette tip 3.

FIG. 10A, FIG. 10B, FIG. 10C, FIG. 10D, and FIG. 10E illustrate variousviews of a pipette tip 3 according to yet another exemplary embodimentof the presently disclosed subject matter. Namely, FIG. 10A is aperspective view, FIG. 10B is a top view, FIG. 10C is a side view, FIG.10D is an end view from the tip end, and FIG. 10E is an end view fromthe wide end of the pipette tip 3. The pipette tip 3 shown in FIG. 10A,FIG. 10B, FIG. 10C, FIG. 10D, and FIG. 10E is one example of a 200 μLpipette tip. Again, while this example is in the context of a 200 μLpipette tip, this particular size is merely exemplary, and other sizesconsistent with the objectives of this disclosure are also contemplated.

The 200 μL-pipette tip 3 includes the pair of conductive electrodes(e.g., the pipette tip electrodes 31 a, 31 b). In this example, thepipette tip electrodes 31 a, 31 b are narrow electrodes that runsubstantially along the full length of the 200 μL-pipette tip 3 and onthe outside surface of the 200 μL-pipette tip 3. Further, each of thepipette tip electrodes 31 terminate near the securing end 33 of the 200μL-pipette tip 3 via a tab (or ear) 30. Namely, the pipette tipelectrode 31 a terminates via the tab (or ear) 30 a. Likewise, thepipette tip electrode 31 b terminates via the tab (or ear) 30 b. Thetabs (or ears) 30 a, 30 b extend beyond the securing end 33 of the 200μL-pipette tip 3. The tabs (or ears) 30 a, 30 b provide the electricalconnection between the 200 μL-pipette tip 3 and the liquid handlingapparatus 1. Again, the pipette tip electrodes 31 a, 31 b are fullyseparated from one another by electrically insulating material 37.

FIG. 11A, FIG. 11B, FIG. 11C, FIG. 11D, and FIG. 11E illustrate variousviews of a pipette tip 3 according to yet another exemplary embodimentof the presently disclosed subject matter. Namely, FIG. 11A is aperspective view, FIG. 11B is a top view, FIG. 11C is a side view, FIG.11D is an end view from the tip end, and FIG. 11E is an end view fromthe wide end of the pipette tip 3. The pipette tip 3 shown in FIG. 11A,FIG. 11B, FIG. 11C, FIG. 11D, and FIG. 11E is another example of a 200μL pipette tip.

The 200 μL-pipette tip 3 shown in FIG. 11A, FIG. 11B, FIG. 11C, FIG.11D, and FIG. 11E is substantially the same as the 200 μL-pipette tip 3shown in FIG. 10A, FIG. 10B, FIG. 10C, FIG. 10D, and FIG. 10E exceptthat the tabs (or ears) 30 a, 30 b do not extend beyond the securing end33 of the 200 μL-pipette tip 3.

FIG. 12A, FIG. 12B, FIG. 12C, FIG. 12D, and FIG. 12E illustrate variousviews of a pipette tip 3 according to still another exemplary embodimentof the presently disclosed subject matter. Namely, FIG. 12A is aperspective view, FIG. 12B is a top view, FIG. 12C is a side view, FIG.12D is an end view from the tip end, and FIG. 12E is an end view fromthe wide end of the pipette tip 3. The pipette tip 3 shown in FIG. 12A,FIG. 12B, FIG. 12C, FIG. 12D, and FIG. 12E is an example of a 200 μLpipette tip wherein the pipette tip electrodes 31 a, 31 b are located onthe inside surface of the 200 μL-pipette tip 3. In some embodiments, asshown in FIGS. 12A-12E, the electrodes 31 a, 31 b are only positioned onan inner surface. However, in other embodiments, pipette tips 3described herein can comprise electrodes on both the inner surface 35and the outer surface 36 of the pipette tip 3. In these embodiments,there are four electrodes, such as a first, second, third and fourthelectrode, where the first and second electrodes are positioned on anouter surface 36 of the pipette tip 3, and the third and fourthelectrodes are positioned on an inner surface 35 of the pipette tip 3.

Further and referring now to FIG. 1 through FIG. 12E, there are manyways of making the presently disclosed pipette tips 3 that are disclosedhereinabove. In one example, the pipette tip 3 can be formed using dualinjection molding processes. In another example, the pipette tip 3 canbe formed using 3D printing processes to print conductive polypropylenestrips onto the side of the tip. In yet another example, the pipette tip3 can be formed according to the method described with reference to U.S.Pat. No. 5,045,286, entitled “Device for aspirating a fixed quantity ofliquid,” issued on Sep. 3, 1991. In still another example, the pipettetip 3 can be formed according to the method described with reference toU.S. Pat. No. 9,346,045, entitled “Electrically conductive pipette tip,”issued on May 24, 2016.

Following long-standing patent law convention, the terms “a,” “an,” and“the” refer to “one or more” when used in this application, includingthe claims. Thus, for example, reference to “a subject” includes aplurality of subjects, unless the context clearly is to the contrary(e.g., a plurality of subjects), and so forth.

Throughout this specification and the claims, the terms “comprise,”“comprises,” and “comprising” are used in a non-exclusive sense, exceptwhere the context requires otherwise. Likewise, the term “include” andits grammatical variants are intended to be non-limiting, such thatrecitation of items in a list is not to the exclusion of other likeitems that can be substituted or added to the listed items.

For the purposes of this specification and appended claims, unlessotherwise indicated, all numbers expressing amounts, sizes, dimensions,proportions, shapes, formulations, parameters, percentages, quantities,characteristics, and other numerical values used in the specificationand claims, are to be understood as being modified in all instances bythe term “about” even though the term “about” may not expressly appearwith the value, amount or range. Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the followingspecification and attached claims are not and need not be exact, but maybe approximate and/or larger or smaller as desired, reflectingtolerances, conversion factors, rounding off, measurement error and thelike, and other factors known to those of skill in the art depending onthe desired properties sought to be obtained by the presently disclosedsubject matter. For example, the term “about,” when referring to a valuecan be meant to encompass variations of, in some embodiments ±100%, insome embodiments ±50%, in some embodiments ±20%, in some embodiments±10%, in some embodiments ±5%, in some embodiments ±1%, in someembodiments ±0.5%, and in some embodiments ±0.1% from the specifiedamount, as such variations are appropriate to perform the disclosedmethods or employ the disclosed compositions.

Further, the term “about” when used in connection with one or morenumbers or numerical ranges, should be understood to refer to all suchnumbers, including all numbers in a range and modifies that range byextending the boundaries above and below the numerical values set forth.The recitation of numerical ranges by endpoints includes all numbers,e.g., whole integers, including fractions thereof, subsumed within thatrange (for example, the recitation of 1 to 5 includes 1, 2, 3, 4, and 5,as well as fractions thereof, e.g., 1.5, 2.25, 3.75, 4.1, and the like)and any range within that range.

Although the foregoing subject matter has been described in some detailby way of illustration and example for purposes of clarity ofunderstanding, it will be understood by those skilled in the art thatcertain changes and modifications can be practiced within the scope ofthe appended claims.

1. A method for automatically maintaining a pipette tip depth in aconductive fluid during a fluid transfer operation, comprising the stepsof: providing a pipetting device, comprising: a pipette tip having asecuring end with an opening, a fluid transferring end with an opening,an outer surface, and an inner surface, wherein the outer surfaceincludes an electrically insulating material; a first and a secondelectrode on the outer surface of the pipette tip, the first and secondelectrode being separated by the electrically insulating material; aframe supporting an actuator that is operatively connected to thepipette tip, wherein the pipette tip is vertically oriented relative tothe frame, and wherein the actuator is adapted to move the height of thepipette tip relative to the frame; and a controller that is inelectrical connection with the first and second electrodes; providing acontainer fixed in height relative to the frame, the container holding aconductive fluid having a first liquid level; positioning the pipettetip in the container such that at least a portion of the first andsecond electrodes are submerged in the conductive fluid, wherein thepositioning step forms a control loop between the first and secondelectrodes, the actuator, the controller, and the conductive fluid;measuring by the first and second electrodes a change in resistancerelative to the conductive fluid; sending by the first and secondelectrodes a signal to the controller relative to the change, whereinthe controller is configured to command the actuator to move the pipettetip vertically in response to the signal.
 2. The method as recited inclaim 1, further comprising the steps of: aspirating by the pipette tipan amount of the conductive fluid, wherein the conductive fluid has asecond liquid level following the aspirating step; commanding by thecontroller the actuator to move the pipette tip relative to the secondliquid level such that the first and second electrodes remain submergedin the conductive fluid.
 3. The method as recited in claim 1, furthercomprising the steps of: dispensing by the pipette tip an amount of theconductive fluid, wherein the conductive fluid has a second liquid levelfollowing the dispensing step; commanding by the controller the actuatorto move the pipette tip relative to the second liquid level such thatthe first and second electrodes remain submerged in the conductivefluid.
 4. The method as recited in claim 1, further comprising the stepof: maintaining by the control loop the pipette tip at a constant secondliquid level relative to the liquid surface of the conductive fluid. 5.A pipette tip, comprising: a body made from an electrically insulatingmaterial, the body comprising: an outer surface, and an inner surface; afirst electrode disposed on the outer surface; and a second electrodedisposed on the outer surface, the second electrode being separated fromthe first electrode by the electrically insulating material.
 6. Thepipette tip of claim 5, wherein the body further comprises: an apparatussecuring end; and an fluid transferring end positioned opposite theapparatus securing end, the fluid transferring end comprising a fluidtransferring opening.
 7. The pipette tip of claim 5, further comprisinga third electrode and a fourth electrode disposed on the inner surface.8. The pipette tip of claims 6, wherein each or all of the electrodesextend along a full longitudinal length of the body from the fluidtransferring end to the apparatus securing end.
 9. The pipette tip ofclaims 6, wherein each or all of the electrodes extend a distance lessthan a full longitudinal length of the body from the fluid transferringend to the apparatus securing end.
 10. The pipette tip of claims 5,wherein each of the electrodes are made of copper or an electricallyconductive polypropylene.
 11. The pipette tip of claim 8, wherein eachelectrode comprises an electrical contact tab positioned on theapparatus securing end of the electrode.
 12. The pipette tip of claim11, wherein the electrical contact tab extends beyond the apparatussecuring end of the pipette tip.
 13. The pipette tip of claim 7, whereineach or all of the electrodes extend along a full longitudinal length ofthe body from the fluid transferring end to the apparatus securing end.14. The pipette tip of claim 7, wherein each or all of the electrodesextend a distance less than a full longitudinal length of the body fromthe fluid transferring end to the apparatus securing end.
 15. Thepipette tip of claim 7, wherein each of the electrodes are made ofcopper or an electrically conductive polypropylene.